Radar system and antenna therefor



Nov. 10, 1953 R. HERB RADAR SYSTEM AND ANTENNA THEREFOR Filed Oct. 10, 1945 lNDlCATQR INVENTOR. RAYMOND G'HERB WQM.

ATTORNEY Patented Nov. 10, 1953 RADAR SYSTEM AND ANTENNA THEREFOR Raymond G. Herb, Boston, Mass., assignor, by mesne assignments, to the United States of America as represented by the Secretary of War Application October 10, 1945, Serial No. 621,569

11 Claims.

This invention relates to antennas for radio object-locating systems and more particularly to an antenna having a reflector and radiating means for illuminating the reflector.

One of the objects of the invention is to provide an antenna having a parabolic reflector with a novel means for radiating and receiving radiant energy in such manner that the elevation angle of a target may be determined without requiring vertical motion of the reflector or of the antenna.

Another object of the invention is to provide in an antenna, having reflecting means and radiating means, means for producing a desired radiation pattern including one in which the energy distribution approximates the relationship csc a in one plane, generally the vertical plane where 0 is the angle measured from the axis of directivity of the reflecting means.

For a better understanding of the invention together with other and further objects thereof, reference is had to the following description, taken in connection with the accompanying drawme.

In the drawing:

Fig. 1 is a perspective view of a typical antenna according to this invention;

Fig. 2 is a perspective view of the feed line and novel radiating means according to one embodiment of the invention;

Fig. ,3 is. a diagrammatic sectional view along the line 33 of Fig. 2;

Fig. 4 is a diagrammatical sectional view of the feed line of Fig. 2 illustrating the positions of the exciting means and also the direction of the principal E-vector of energy within the feed line; and Fig. 5 is a diagrammatic side elevation of the antenna of Fig. 1 illustrating the radiation pattern produced thereby and geometry of the invenion.

Referring now to Fig. 1, there is shown an antenna comprising a reflector I 0 which may be of any suitable conformation such as a paraboloid of revolution, a truncated paraboloid, or a parabolic cylinder or any other suitable shape to direct energy from or to a radiating element. As shown, reflector I0 is, for example, a truncated paraboloid supported on a base II and, if desired, in such manner that reflector It may be rotated about either a vertical or horizontal axis, or both. For simplification of description, it is assumed herein that reflector I0 is immovably secured to base I I with the plane of its aperture vertical and with the longitudinal axis thereof horizontal. A radiating element I2 is mounted in front of and 2 at a suitable distance from reflector ID for illuminating the latter.

According to this invention, radiating element I2 comprises a hollow pipe waveguide I3 of substantially circular cross-section adapted to support only the TE1,1 mode of energy and is disposed with its axis perpendicular to the focal axis of reflector I0. In the arrangement as shown in Fig. 1, waveguide I3 is disposed with its axis vertical and is supported in any suitable manner such as by brackets I4 secured to waveguide I3.

Waveguide I 3 (Figs. 2 and 3) is electrically connected at or near one end (in this case the lower end) with apparatus for transmitting and receiving waves of electromagnetic energy. Thus, waveguide I3 is provided with coupling means I5 for connection with the transmitting apparatus as indicated by T and coupling means I6 and I! for connection with two receiving apparatus designated R1 and R2 respectively. Coupling means I5, I6, and I 1 may be of any suitable design for exciting and picking up energy within Waveguide [3. For example, means I5 may comprise an exciting probe I5 fed by a waveguide or transmission line I5" while coupling means I6 and Il may be in the form of pick-up probes or loops I6 and Il coupled to transmission lines I6" and I1". Transmission lines I5", I6" and I1" may be of the hollow pipe waveguide or coaxial conductor type. Means I5, I6 and "are preferably spaced circumferentially about wave guide I3 in such manner that the axis of the coupling loops or probes .15, I6 and I1 (Fig. 3) extend radially into waveguide I3 for a purpose more clearly described hereinafter.

Arranged along a portion of the length of waveguide I3 are a plurality of aligned dipoles I8. As shown more clearly in Fig. 2, there are 10 dipoles [81-4810 arranged in a vertical straight line so that a plane passing through the longitudinal axis of Waveguide l3 and the row of dipoles l8 will contain the focal axis of reflector I0 and is substantially perpendicular to the aperture plane of reflector H), with the row of dipoles I8 being disposed nearest reflector Ill.

Radiating element I2 may be disposed in any desired position along the axis of waveguide I3 depending upon the shape of the desired pattern and whether the main path of the desired beam pattern is to be directed ahead of the reflector or above 01' below the reflector axis. Thus, for airborne use with the antenna depending for example from the belly of an aircraft, it is desired to direct the radiation pattern in a downward direction or toward the ground. For such use, radiating element I2 would be disposed above, or at least with the majority of the dipoles I8 above, the reflector axis. However, the principal application of an antenna as herein described is in searching for, or tracking oi, airborne targets from a ground station. Thus, as shown in Figs. 1 and 5, radiating element I2 is disposed below the axis H of reflector IE1 or with the majority of dipoles I8 below the axis H and preferably with the uppermost dipole l8, on or slightly below axis H at the approximate focal point F. For simplification of description and by way of example, the description of the invention herein is directed to such an arrangement.

Dipoles IS may be of any conventional design adapted to radiate and receive waves of electromagnetic energy towards or away from reflector I0. Energy to and from each of dipole I8 is transmitted by means of a transmisison line I9 and by a stub line 23 preferably .angularly disposed relative to the line I 9, lines I9 and 2B preferably. being of the coaxial conductor type as shown (Fig. 3), Each stub line 20 is coupled to the region of propagation within waveguide I3 by means of a radially disposed probe 2I adapted to excite or pick-up energy in waveguide I3.

While dipoles I81-I81u are arranged in a straight line along waveguide I3, probes 2I are so arranged that successively they enter waveguide 3 at gradually increasing angles or grad- Y ually increasing.circumferential distances toward one endof waveguide I3 relative to the position of their respective dipoles (Fig. 4). Preferably, the probe 2I at the uppermost end of waveguide I3 is disposed at a small or 0 angle with respect to its corresponding dipole I81, While the remaining probes 2I are disposed in turn at'increasing angles or circumferential distances relative to their corresponding dipoles, with the probe 2| nearest the lowermost part of waveguide I3 being preferably approximately 90, from its corresponding dipole I810. The relative position of the dipoles I8 and their respective probes 2I is, accomplished by making the connecting transmission lines ,IS progressively longer and preferably curving the same to follow the contour of waveguide I3.

Assuming that the exciting probe I5 of coupling means I5 is substantially in alignment with the row of dipoles I8 and with probe 2| coupling dipole I81 to waveguide I3, the maximum E- vector (designated E in Fig. 4) or the E-vector in the axis of symmetry of the TE1.1 mode within waveguide I3 will be substantially coincident with the 0-180 line or in other words, coincident with the radius to probe 2! serving dipole I81. Thus, probe 2I of uppermost dipole I81 will be strongly coupled to the electrostatic field in the waveguide I3 while the remaining probes 2| will have relatively and progressively weaker coupling and probe 2! for the lowermost dipole I810 will have very weak coupling.

Therefore, when the antenna is being utilized for radiation of energy, the intensity or amplitude of radiation from dipoles I8 and of the intensity of illumination of reflector I6 is tapered due to the graduated coupling of probes 2|, the greater intensity being radiated from the uppermost dipole I 81, and the least from the lowermost dipole I810. By properly adjusting the depth of penetration of probes 2I into waveguide I3, any desired resultant radiation pattern may be produced including one of csc fl configura- 4 tion as indicated by the solid line pattern in Fig. 5.

On reception of energy, such as return of echo pulses from targets, the maximum energy returned from a low target and rereflected by reflector I 6 will be received by the upper dipoles I8 while that from the high targets will be received by the lower dipoles I8. Thus, from Fig. I5, it will be seen that the energy returned by a target T1 of high elevation is reflected by reflector I0 and will be received by and. excite maximum energy in dipole I810, also the energy from a target of low elevation T2 will be returned with maximum intensity to dipole I81, the returning energy being indicated by broken lines in Fig. 5. Since the elevation of the target with reference to the antenna determines which of dipoles I8 receives most of the incoming energy and since each dipole excites energy in waveguide I3 through probe 2| with a characteristic polarization determined by the relative circumferential position of the respective probes 2 I, the resultant direction of the E-vector of the energy excited in waveguide I3 is a function of the elevation angle of the target. Fig. 4 shows the orientation of the maximum Ef-vector when maximum energy intensity is received by dipole I85, the posi tion of which is shown in Fig. 3. By placing the two receiver channels or coupling means I5 and I! in spaced circumferential relation about waveguide I3 as disclosed hereinbefore, the orientation of the electrostatic field in waveguide I3 and consequently, the elevation of the target can be found by comparison on a suitable indicator 22 of the magnitudes of the two received outputs. Any suitable known type of receiver may be utilized with the antenna as herein described ranging from those having two complete amplifiers to those with a single detector and amplifier with the addition of a switch or delay line to separate the energy pulses to be compared.

While the present invention has been particularly described with the radiating element I2 oriented vertically to determine elevation, it will be understood that by orienting the antenna conducting the radiating element I2 horizontally, the angle of a target in azimuth may also be determined.

What is claimed is:

1. A system comprising an antenna having a parabolic reflector and a waveguide of circular cross-section adapted to entertain the TE1,1 mode of electroma netic energy, said waveguide being positioned with its axis substantially perpendicular to the focal axis of said reflector, a plurality of aligned and equally spaced dipoles arranged along a portion of the length of said waveguide and parallel to the waveguide axis, means for coupling each of said dipoles to the region of propagation within said waveguide, one of said coupling means being substantially aligned radially with the first of said aligned dipoles, each of said remaining coupling means being spaced circumferentially about said waveguide from its respective dipole, the spacing between said remaining coupling means and said dipoles progressively increasing toward one end of said waveguide and away from said first dipole, means electrically connecting said dipoles and said coupling means and supporting said dipoles, and means for exciting energy in the TE'1,1 mode in said waveguide, said exciting means being positioned near one end of said waveguide in alignment with one of said coupling means, whereby the latter is adapted to have maximum coupling and the remaining coupling means have relatively weaker coupling to the energy excited in said waveguide resulting in unequal intensity of energy radiated from said dipoles for producing an unsymmetrical radiation pattern.

2'. The system defined in claim 1 wherein each of said coupling means includes a probe extending radially into said waveguide, the depth of penetration of said probes determining the radiation intensity from each of said dipoles and thus producing a desired pattern of radiation from the antenna.

3. The system defined in claim 1 wherein said coupling means are adapted to be so arranged relative to the electromagnetic field of energy within said waveguide that the energy distribution pattern radiated by said antenna varies substantially as the square of the cosecant of the radiation angle measured from the axis of directivity of said reflector.

4. A system defined in claim 1 wherein said means to excite said wave guide may be periodically energized whereby a pulse may be transmitted by said antenna, said dipoles being so positioned relative to said reflector that radiant energy returned as an echo to said antenna by a target is directed by said reflector onto said aligned dipoles, the angle of elevation of said target determining which one of said dipoles receives, and which of said coupling means excites in said waveguide, energy of maximum intensity, the relative position of said last-mentioned coupling means thereby determining the orientation of the maximum E-vector of energy in said waveguide, and wherein two coupling means are spaced from each other about one end portion of said waveguide, said two coupling means being adapted to be excited by said energy in said waveguide, the orientation of the maximum E-vector determining the relative intensity of energy picked up by said two coupling means, whereby, by comparison of the outputs of said two coupling means, the orientation of the maximum E-vector and consequently the elevation of the target is determinable.

5. A system for radiating and receiving waves of electromagnetic energy comprising in combination, a parabolic reflector and a waveguide of substantially circular cross-section for entertaining the 'I'E1,1 mode of energy propagation, said waveguide being positioned with its axis substantially perpendicular to the focal axis of said parabolic reflector near the focal point thereof, a plurality of aligned dipoles arranged along a portion of the length of said waveguide and parallel to said waveguide axis, means for coupling each of said dipoles to the region of propagation within said waveguide, one of said coupling means being substantially aligned radially with the first of said aligned dipoles, each of the remaining coupling means being spaced circumferentially about said waveguide from its respective dipole, the spacings between said coupling means and said dipoles progressively increasing towards one end of said waveguide and away from said first dipole, means electrically connecting each of said dipoles to its coupling means, means for exciting energy in the TE1,1 mode within said waveguide, said exciting means being so positioned that the maximum E-vector of the energy excited thereby is in radial alignment with one of said coupling means, and output means coupled to said waveguide responsive to the orientation of the maximum E-vector pro- 6 duced by received energy for determining the elevation angle of said received energy.

6. A system comprising an antenna having parabolic reflecting means, a waveguide of suitable shape and dimensions for entertaining the TE1.1 mode of electromagnetic energy, a plurality of dipoles arranged to constitute a linear antenna array along a portion of the length of said waveguide, means positioning said array in a plane substantially perpendicular to the focal axis of said reflecting means, means for periodically exciting energy of the TE1,1 mode in said waveguide, whereby a pulse willbe radiated by said antenna, means for coupling each of said dipoles to the region of energy propagation with in said waveguide, each of said coupling means being adapted to be excited by energy in said waveguide of varying degrees of intensity depending on the position of said coupling means relative to the energy field in said waveguide and to excite in said waveguide energy of varying degrees of intensity depending on which of the respective dipoles receives energy of maximum intensity returned by a target to said antenna during the period that said exciting means is inoperative,, and means coupled to said waveguide for determining the orientation of the maximum E-vector of received energy in said waveguide and consequently the angle of elevation of the target returning said returned energy.

'7. A system comprising a plurality of dipoles aligned along a wave guide, means to couple successive dipoles to successive points within said wave guide, said points being characterized by an increased peripheral displacement from the aligned dipoles, means to excite said wave guide in the transverse electric mode with pulses of carrier wave energy, said means being aligned with said dipoles, and means circumferentially spaced from said exciting means to determine the angle of polarization of energy induced within said wave guide by a pulse echo.

8. In a pulse echo system, an antenna comprising a parabolic reflector, a wave guide, a plurality of dipoles disposed along the surface of said wave guide and aligned with a longitudinal axis thereof, means to mount said wave guide and the array of said dipole perpendicular to the axis of said reflector, the uppermost of said dipoles being positioned at the focal point of said reflector, a plurality of wave guide probes to electrically connect each of said dipoles to said wave guide, the probe complementary to said uppermost dipole being substantially perpendicular thereto, successive probes being spaced increasingly greater peripheral distances from their respective complementary dipoles, the peripheral spread between the uppermost and the lowermost of said probes being less than degrees, means to excite said wave guide in the transverse electric mode with pulses of carrier wave energy, said exciting means being aligned with said aligned dipole array, whereby a pulse of electromagnetic energy radiated by said dipoles may be directed from said reflector in an unsymmetrical pattern, and means to determine the polarization of a field set up in said wave guide by an echo resulting from the aforesaid radiated energy being reflected from a target back to said antenna, whereby the elevation angle of said target may be determined.

9. An antenna comprising waveguide means, a linear array of antenna elements, a number of probes situated within said waveguide, said probes situated within said waveguide, said probes '2 having different angular positions of entry into said waveguide with respect to a reference posi tion, and means separately coupling each of said probes to a difierent one of said antenna elements.

10. An antenna system comprising a reflector, an array of spaced antenna elements juxtaposed to said reflector, a waveguide, an array of probes situated within said waveguide, said probes having difierent angular positions of entry into said waveguide with respect to a reference direction, and means coupling each of said probes to one of said antenna elements.

11. An antenna system comprising a reflector, a plurality of spaced antenna elements cooperating with said reflector, a Waveguide, a like plurality of probes situated within said waveguide, said probes having difierent angular positions in said waveguide, each of said probes being separately coupled to a corresponding antenna element, and means coupled to said waveguide to transmit energy to and from said waveguide.

RAYMOND G. HERB.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,129,712 Southworth Sept. 13, 1938 2,156,653 llberg May 2, 1939 2,206,923 Southworth July 9, 1940 2,429,601 Biskeborn et a1. Oct. 28, 1947 2,432,990 Hansen Dec. 23, 1947 2,464,276 Varian Mar. 15, 1949 2,478,242 Clapp Aug. 9, 1949 2,480,208 Alvarez Aug. 30, 1949 

